1. Field of the Invention
The present invention relates to a circuit breaker having superior shock and vibration resistance.
2. Discussion of Related Art
As shown in FIG. 6, a circuit breaker having the following configuration has already been proposed (see Japanese Patent Application Laid-open No. Hei-1-166435). Specifically, when a handle 1 is pivoted from an off (OFF) position to an on (ON) position, a circuit is closed by bringing a movable contact point into contact with a fixed contact point via a lever mechanism A. Further, the lever mechanism A and the handle 1 are constrained in the ON position. In contrast, when a movable iron piece 3 is attracted to an electromagnetic trip coil 2 by application of a signal such as an overcurrent to the electromagnetic coil 2, the lever mechanism A is released from the constrained state, and the movable contact point is separated from the fixed contact point, thereby opening the circuit. Further, the handle 1 returns to the OFF position in conjunction with the lever mechanism A.
In a case where the foregoing circuit breaker is provided on an automobile, the movable iron piece 3 moves in the direction-in which it is supposed to be attracted to the coil-due to abnormal physical shock or vibration, whereby the lever mechanism A is accidentally released from a constrained state. As a result, the movable contact point is separated from the fixed contact point, thereby resulting in a risk of the circuit breaker erroneously carrying out tripping action.
Such a problem may be avoided, so long as a spring 4 is provided for holding the movable iron piece 3 in a non-attraction position more firmly, and the spring force of the spring 4 is increased. However, the electromagnetic trip coil 2 is required to have an attracting force sufficient to overcome the spring force, thereby rendering the circuit-breaking operation of the breaker unstable and resulting in a decrease in the reliability of the circuit breaker.
The handle 1 itself is pivoted from the ON position to the OFF position due to abnormal physical shock or vibration. Accordingly, there may arise a risk of the circuit breaker erroneously causing a tripping operation, as in the foregoing case.